We plan to determine effects of opioids on growth of salamander limbs and on development of young mice. These studies will include biochemical and morphological parameters. For the biochemical studies we plan to determine incorporation of labeled uridine and thymidine. Electron microscopical studies will be done on nerves and ganglia of growing mice treated from birth with opioids. Further studies on the discrimination of opioid receptors for analgesia and respiration will continue. We hope to identify these receptors or tracts by stereotaxic ablation techniques.